//iterate while there are instructions and no children tasks
while(!stack.empty() && children.size() <= 0){
//pop the instruction and interpret it
Instruction inst = stack.pop();
strace= inst.getSkeletonTrace(); //skeleton trace in case of exception
P = inst.interpret(P, stack, children);
//check that the task has not been canceled
if(task.isCancelled()) return task;
}